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Homework Help: Need java stack help

  1. Nov 5, 2011 #1
    First i create simple claculator.but now I am trying to change it to RPN calculator by using stack.Can some one help me((especially where to use pop method) because I don't know alot about stack.here is my codes so far.

    Code (Text):
    import java.awt.event.*;

    import javax.swing.*;

    import javax.swing.event.*;
    import java.util.Scanner;

    public class CalcGUIPanel extends JPanel

    Stack s=new Stack();

    //--\- Component referenced during execution

    private JTextField displayField; // display result / input.

    //--\- Variables representing state of the calculator

    private boolean startNumber = true; // true: num key next

    private int resultValue = 0; // result so far

    private String previousOp = "="; // previous operation

    //========================================= static (class) variables

    private static final Font BIGGER_FONT =

    new Font("monspaced", Font.PLAIN, 20);

    //====================================================== constructor

    public CalcGUIPanel()

    //--\- Display field

    displayField = new JTextField();

    //--\- Clear button

    JButton clearButton = new JButton("CLEAR");


    clearButton.addActionListener(new ClearListener());

    //--\- One listener for all numeric keys.

    ActionListener numListener = new NumListener();

    //--\- Layout numeric keys in a grid. Generate the buttons

    // in a loop from the chars in a string.

    String buttonOrder = "789456123 0 ";

    JPanel buttonPanel = new JPanel(new GridLayout(5, 3));

    for (int i = 0; i < buttonOrder.length(); i++) {

    String keyTop = buttonOrder.substring(i, i+1);

    if (keyTop.equals(" ")) {

    buttonPanel.add(new JLabel(""));

    } else {

    JButton b = new JButton(keyTop);






    //--\- One ActionListener to use for all operator buttons.

    ActionListener opListener = new OpListener();

    //--\- Create panel with gridlayout to hold operator buttons.

    // Use array of button names to create buttons in a loop.

    JPanel opPanel = new JPanel(new GridLayout(5, 1));

    String[] opOrder = {"+", "-", "*", "/", "enter"};

    for (int i = 0; i < opOrder.length; i++) {

    JButton b = new JButton(opOrder[i]);






    //--\- Layout the top-level panel.

    this.setLayout(new BorderLayout());

    this.add(displayField, BorderLayout.NORTH );

    this.add(buttonPanel , BorderLayout.CENTER);

    this.add(opPanel , BorderLayout.EAST );

    this.add(clearButton , BorderLayout.SOUTH );

    }//end constructor

    //====================================================== action_clear

    /*\* Called by Clear btn action listener and elsewhere.*/

    private void action_clear() {

    startNumber = true;


    resultValue = 0;

    previousOp = "=";


    // inner listener class OpListener

    /*\* Listener for all op buttons. \*/

    class OpListener implements ActionListener {

    public void actionPerformed(ActionEvent e) {

    // The calculator is always in one of two states.

    // 1. A number must be entered \-\- this operator is wrong.

    // 2. An operator must be entered \-\- we're ok.


    startNumber = true; // Next thing must be a number

    try {

    // Get value from display field, convert, do prev op

    // If this is the first op, \_previousOp will be =.

    String displayText = displayField.getText();

    int currentValue = Integer.parseInt(displayText);

    if (previousOp.equals("=")) {

    resultValue = currentValue;

    } else if (previousOp.equals("+")) {

    resultValue += currentValue;

    } else if (previousOp.equals("-")) {

    resultValue -= currentValue;

    } else if (previousOp.equals("*")) {

    resultValue *= currentValue;

    } else if (previousOp.equals("/")) {

    resultValue /= currentValue;



    } catch (NumberFormatException ex) {




    //--\- set \_previousOp for the next operator.

    previousOp = e.getActionCommand();

    }//endif \_startNumber


    }//end class

    //////////////////////////////////// inner listener class ClearListener

    // Action listener for numeric keys

    class NumListener implements ActionListener {

    public void actionPerformed(ActionEvent e) {

    String digit = e.getActionCommand(); // Get text from button

    if (startNumber) {

    // This is the first digit, clear field and set


    startNumber = false;

    } else {

    // Add this digit to the end of the display field

    displayField.setText(displayField.getText() + digit);



    }//end class

    //inner listener class ClearListener

    class ClearListener implements ActionListener {

    public void actionPerformed(ActionEvent e) {




  2. jcsd
  3. Nov 5, 2011 #2


    Staff: Mentor

    OK, so tell us what you know about how an RPN calculator should work.

    What should happen if you want to add two numbers?
    What should happen if you want to subtract two numbers?
    What should happen if you want to multiply two numbers?
    What should happen if you want to divide two numbers?
    What should happen if you want to change the sign of a number?
    What should happen if you want to square a number?
  4. Nov 5, 2011 #3
    To subtract two numbers it should be like this
  5. Nov 5, 2011 #4


    Staff: Mentor

    OK, fine. Since your program is using a stack to implement an RPN calculator, here's what your program should do.
    User: press 7 then press Enter.
    User: press Enter key.
    Program: push 7 onto stack.
    User: press 1 then press Enter.
    Program: push 1 onto stack.
    User: press - key.
    Program: pop top of stack (1), pop top of stack (7), calculate 7 - 1, display 6.

    The other three arithmetic operations are similar.
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